In a so-called top-mount-type airbag device for a passenger's seat that is provided at an opening portion of a substantially flat top surface of an instrument panel, there is known a technique of providing an inner bag for controlling the flow of gas to the airbag interior (see, for example, Japanese Patent Application Laid-Open No. 11-170955). In this airbag device, while a gas supply is received through an inner bag that is expanded first, the airbag is expanded so as to squeeze-out between the inner bag and a windshield glass or the instrument panel, and the speed of expansion of the airbag is reduced.
Further, in addition thereto, there are known structures, in an airbag device for a passenger's seat, in which various contrivances have been made with respect to the expanded form of the airbag before restraining the passenger (see, for example, Japanese Patent Application Laid-Open No. 51-23917, Japanese Patent Application Laid-Open No. 2007-106376, Japanese Patent Application Laid-Open No. 2007-161201, Japanese Utility Model Application Laid-Open No. 7-17662, Japanese Patent Application Laid-Open No. 2007-045190, Japanese Patent Application Laid-Open No. 2007-062455).